Integrated circuits include several types of components, particularly transistors. Various types of transistors may be formed using various techniques. Two examples of transistors are a Metal Oxide Semiconductor Field Effect Transistor (MOSFET) and a Bipolar Junction Transistor (BJT). Both devices have various advantages and disadvantages that make one type of device preferable in some cases and not preferable in other cases.
MOSFET devices include a gate structure on top of a semiconductor substrate. Both sides of the gate structure are then doped to form source and drain regions. A channel is formed between the source and drain regions beneath the gate. Based on the voltage bias applied to the gate, electric current may either be allowed to flow through the channel or be inhibited from doing so.
In some cases, the channel may be formed using a fin structure. The fin structure extends out of the substrate and runs perpendicular to the gate structure formed on the substrate and fin structures. Such devices are sometimes referred to as finFET devices. FinFETs provide various advantages which are outside the scope of the present discussion.
Typical BJT layouts include concentric, polygonal rings surrounding a solid polygonal piece in the middle. The solid piece in the middle is typically the emitter terminal. A first polygonal ring surrounding the solid piece is the base terminal, and a second polygonal ring surrounding the first polygonal ring is the collector terminal. In such a structure, electric current flowing between the emitter terminal and the collector terminal flows in many directions from the inner solid piece in an outward direction towards the polygonal rings.
It may be beneficial to have a circuit that utilizes both MOSFET type devices and BJT type devices. However, because different processes are typically used to form BJT devices, having both BJT and MOSFET type devices in the same circuit can be more costly and time consuming to produce. Therefore, it is desirable to have an efficient BJT structure that is compatible with the finFET fabrication process.